The present invention relates to an electrostatic image developing toner which is employed in copiers and printers, a production method of said toner, and an image forming method using said toner.
Recently, Japanese Patent Publication Open to Public Inspection No. 2000-214629 disclosed that since it is possible to control the diameter as well as the shape of polymerization toner particles, prepared utilizing a suspension polymerization method or an emulsion polymerization method, during the polymerization process in a water based medium, it is possible to prepare minute spherical toner particles having no corners as well as having a narrow size distribution. Said toner has received attention as a toner which makes it possible to reproduce minute dot images for the use of digital images due to its fine line reproducibility as well as excellent definition.
It is known that the dispersibility of coloring agents, which are incorporated into said polymerization toner, is inferior to those of a pulverized toner. This is due to the following factors. In said suspension polymerization method, polymerization is carried out after dispersing pigments as the coloring agents into a monomer. As said polymerization proceeds, said coloring agents coagulate due to an increase in the viscosity of monomer droplets. Further, in said emulsion polymerization method, during polymerization, namely coagulation process, since the effects of the pH accelerate coagulation, said coloring agents coagulate.
As mentioned above, said polymerization toner exhibits problems such that dispersibility is degraded due to the occurrence of the coagulation of coloring agents during the production processes. Therefore, techniques to improve the dispersion of said coloring agents have been increasingly investigated, however a technique, which overcomes dispersion problems of said coloring agents, has not been found yet. In a multicolor image forming method, color images are formed by superimposing a plurality of toner images, whereby a certain degree of transparency is required. Therefore, when images are formed on film for overhead projectors, said problems become critical.
Further, in said polymerization toner, surface active agents, as dispersing agents, and the like, which are employed in production processes, remain on the surface of toner particles as the final product. As a result, these residual materials cause problems such that the charge holding function of toner varies and toner results in brittleness due to the fact that said residual particles absorb moisture from the ambient air; particularly at high temperature and high humidity, fogging occurs; and resolution is degraded due to dust formed by the destruction of toner during development as well as transfer.
Further, when at high temperature and high humidity, an image forming apparatus is not operated for an extended period of time, a state is formed in which a toner having a varied amount of static charge due to the absorption of moisture and a fresh toner are mixed. As a result, problems occur in which uneven density results on halftone images comprised of halftone dots, and in multicolor image formation, color difference is increased due to difference in developability between developers of each color, which are further affected by said coloring agents incorporated in the toner of said developers.
In order to overcome said problems with residual materials on the surface of toner particles, Japanese Patent Publication Open to Public Inspection No. 57-15085 discloses a technique to decrease the amount of impurities on the surface of toner particles to less than or equal to the specified amount by repeatedly washing the prepared toner. However, the process, which employs a large amount of water for said washing, is not preferred because said process makes the toner production processes more complicated, and in addition, new problems occur in regard to the environmental protection.
It is generally well known that the state of coloring agents incorporated in a toner particle affects the performance of the toner such as resolution. For example, Japanese Patent Publication Open to Public Inspection Nos. 2000-81735 and 2000-284540 disclose that excellent color reproduction as well as static charge stabilizing properties is obtained by improving the dispersibility of a coloring agent in a toner by specifying the ratio of the length to breadth of the particle of said coloring agent as well as the number average diameter of said coloring agent particles employed in a pulverized toner. However, said patents only specify the coloring agent prior to incorporation into toner particles and do not suggest the state of said coloring agent in the toner particle.
Further, when a coloring agent is uniformly dispersed in a toner particle without resulting in a phase separation structure such as a domain structure or a coagulation structure, the resultant transparency is superior, while the resultant static charge holding function tends to be degraded. On the other hand, when said coloring agent is dispersed so as to result in phase separation structure or coagulation, the resultant static charge holding function is excellent, while light transmission is degraded. Japanese Patent Publication Open to Public Inspection No. 5-88409 discloses a capsule toner in which a coloring agent is coagulated into one lump in a particle and a resin covers the resultant lump so as to form a capsule. From the disclosed structure, it was expected that the desired light transmission as well as the desired static charge holding function would be exhibited. However, the desired transparency was not obtained due to the fact that light was scattered at the interface between the coloring agent region and the resin. As noted, a polymerization toner, which exhibits the desired static charge holding function as well as the desired transparency, has not yet been introduced into the market.
A first object of the present invention is to provide an electrostatic image developing toner which is not affected by a residual material present on the surface of toner particles and does not result in variation of the amount of static charge at high temperature as well as at high humidity.
A second object of the present invention is to provide an electrostatic image developing toner to form multicolor images, which results in suitable dispersibility of a coloring agent into a toner particle and also results in light transmission images with high transparency, and results in especially high quality images for overhead projectors.
A third object of the present invention is to provide an electrostatic image developing toner which results in uniform density of halftone images under such operation conditions, of an image forming apparatus, as repetition of non-operation over a relatively long period.
A fourth object of the present invention is to provide an electrostatic image developing toner capable of invariably producing multicolor images with minimal color difference while being not affected by a coloring agent incorporated in each color developer, at high temperature as well as at high humidity, and in an image forming apparatus which has not been operated over an extended period of time.
A fifth object of the present invention is to provide an electrostatic image developing toner capable of consistently producing, over an extended period of time, high quality images which do not exhibit blocked text but exhibit excellent developability as well as excellent reproducibility of fine lines, irrespective of the environment and conditions in which an image forming apparatus is employed.
A sixth object of the present invention is to provide a method for specifically forming digital multicolor images while employing said electrostatic image developing toner.
The present invention not only has simply improved the dispersibility of said coloring agent in toner particles, but has also made it possible to achieve the aforesaid objects. Namely, attention was paid to the structure of the polymerization toner prepared by coalescing resinous particles with toner particles. The coloring agent forms domains in said toner particles. Even though impurities, such as surface active agents, remain on the toner particle, the electrostatic image developing toner, in which domains comprised of said coloring agent are formed in the toner particle and the resultant domains comprised of said coloring agent having an optimal dispersion structure, makes it possible to exhibit a charge holding function without being affected by these effects and to form excellent images such as images with excellent transparency for overhead projectors.
When the components of said coloring agents form domains in the binding resin, and said domains have an optimum dispersion structure in a particle, an electrostatic image developing toner can be prepared which exhibits the advantages described below. Said toner does not result in variation of the amount of toner static charge such as a leak of static charge amount during standby even under employed conditions at high temperature and high humidity, or under conditions in which an image forming apparatus is used after a long interval of rest, and in addition, does not result in fogging, uneven density of halftone images, and color difference variation in multicolor images, and forms highly transparent color images for overhead projectors.
When water-dampened coloring agents in paste are employed as said coloring agents, the transparency is further improved and the variation of color difference is also further minimized.
The present invention, as well as embodiments thereof, will now be described.
1. In an electrostatic image developing toner comprising a coloring agent and toner particles, said toner particles have a matrix-domain structure, and the average of the area of a Voronoi polygon formed by the perpendicular bisecting line between the centers of gravity of domains adjacent to each other in said matrix-domain structure is from 20,000 to 120,000 nm2, and the variation coefficient of the area of said Voronoi polygon is less than or equal to 25 percent.
2. The electrostatic image developing toner, described in 1, above, wherein the average of the area of said Voronoi polygon formed by the perpendicular bisecting line between the centers of gravity of domains adjacent to each other in said matrix-domain structure is from 40,000 to 100,000 nm2, and the variation coefficient of the area of said Voronoi polygon is less than or equal to 20 percent.
3. The electrostatic image developing toner, described in 1 or 2 above, wherein the average of the area of said Voronoi polygon formed by the perpendicular bisecting line between the centers of gravity of domains adjacent to each other in said matrix-domain structure is from 20,000 to 120,000 nm2, and the umber ratio of the domain, which forms said Voronoi polygon having an area of at least 160,000 nm2, is from 3 to 20 percent of the total number of domains.
4. The electrostatic image developing toner, described in 1. through 3. above, wherein the average of the area of a Voronoi polygon formed by the perpendicular bisecting line between the centers of gravity of the domains in the exterior of a 1,000 nm radius circle having the center of gravity in the cross-section of said toner particle as the center is smaller than the average of the area of a Voronoi polygon formed by the perpendicular bisecting line between the centers of gravity of said domain in the interior of said circle.
5. The electrostatic image developing toner, described in 1. through 4. above, wherein of Voronoi polygons formed by the perpendicular bisecting line between the centers of gravity of the domains adjacent to each other in said matrix-domain structure, the number ratio of Voronoi polygons having an area of at least 160,000 nm2 which come into contact with the external circumference of said toner is from 3 to 20 percent of the total number of said domains.
6. The electrostatic image developing toner, described in 1. through 5. above, wherein said toner particle is comprised of a matrix-domain structure and has a region comprising no domain portion of a length of 500 to 6,000 nm as well as a height of 100 to 200 nm along the circumference of the cross-section of said toner particle.
7. The electrostatic image developing toner, described in 1. through 6. above, wherein said domains are comprised of ones having different luminance.
8. The electrostatic image developing toner, described in 1. through 7. above, wherein said resin forms the portion corresponding to said matrix, and said coloring agent forms the portion corresponding to said domain.
9. The electrostatic image developing toner, described in 1. through 8. above, wherein said coloring agent is prepared employing a water-dampened coloring agent paste.
10. The electrostatic image developing toner, described in 1. through 9. above, wherein said toner has a number variation coefficient of less than or equal to 27 percent in the number particle size distribution, and also has a variation coefficient of the shape factor is less than or equal to 16 percent.
11. The electrostatic image developing toner, described in 1. through 10. above, wherein said toner is comprised of toner particles without corners of at least 50 percent by number, and has a number variation coefficient in the number particle size distribution of less than or equal to 27 percent.
12. The electrostatic image developing toner, described in 1. through 11. above, wherein said toner is comprised of toner particles having a shape factor of 1.2 to 1.6 of at least 65 percent by number, and has a particle number variation coefficient, in the number particle size distribution, of less than or equal to 27 percent.
13. The electrostatic image developing toner, described in 1. through 12. above, wherein said toner is comprised of toner particles having a number average particle diameter of 3 to 9 xcexcm.
14. The electrostatic image developing toner, described 1. through 13. above, wherein said toner has a sum (M) of at least 70 percent, wherein said sum (M) consists of relative frequency (m1) of toner particles which are included in the most frequent class and relative frequency (m2) of toner particles which are included in the second most frequent class in the histogram which shows the particle size distribution based on the number of particles, which is drawn in such a manner that regarding said toner, when the particle diameter of toner particles is represented by D (in xcexcm), natural logarithm in D is taken as the abscissa, and said abscissa is divided into a plurality of classes at an interval of 0.23.
15. The electrostatic image developing toner, described in 1. through 14. above, wherein said toner is prepared by salting-out/fusing resinous particles prepared via a process of polymerizing a polymerizable monomer and coloring agent particles.
16. The electrostatic image developing toner, described in 1. through 15. above, wherein said resinous particles are prepared by polymerizing a polymerizable monomer in a water based medium.
17. The electrostatic image developing toner, described in 1. through 15. above, wherein said toner particles are prepared by aggregating and fusing resinous particles and coloring agent particles in a water based medium.
18. The electrostatic image developing toner, described in 1. through 15. above, wherein said toner particles are prepared by salting out/fusing resinous particles prepared by a multi-step polymerization method and coloring agent particles.
19. The electrostatic image developing toner, described in 1. through 18. above, wherein said toner particles are comprised of a resinous layer which is formed by fusing resinous particles comprising a crystalline material, toner particles, and resinous particles comprised of a resin having a lower molecular weight than the resin of said resinous particles, employing a salting-out/fusion method.
20. In an image forming method comprised of processes in which an electrostatic latent image, formed on a photoreceptor, is visualized employing a developer, and said visualized image is transferred onto a recording medium and thermally fixed, an image forming method wherein said thermal fixing is carried out employing a fixing unit having a looped belt-shaped film.
21. The image forming method, described in 20. above, wherein an electrostatic latent image is formed utilizing digital exposure onto a photoreceptor.